Dear Mr. Malhotra,
First of all let us discuss the sancity of the Affidiavit.
Affiidavit is not included in the Definition of "Evidence" as mentioned under section 3 and can be used in evidence only if the court permits it to be so used for sufficient reasons.
But it still holds good as admission under section 18 to 21 of Indian Evidence Act.
You have not specified if the GPA and will is registered or not. However even if it is unregistered, it will still holds good at the intial level and thereafter you have to use it during cross examination to prove your case.
At this juncture, the question is what is the requirment of your client. If he wants he money back with damages and interest than you can file a suit for the same without going into the specific performance of the agreement.
You are also free to approach the court for specific performance of the contract and for an injunction during the continuance of proceedings along with damages and compensation. What is worth mentioning is that you have to specifically pray for stay, damages and compensation or else court will not be able to grant it.
Regards